1. The Field of the Invention
The present invention relates to a centrifugal separator system for treating water that has been contaminated with both organic and inorganic materials. In one embodiment, the present invention relates to a rotating pressure vessel that separates solids and liquids at a high rate. In another embodiment, the present invention relates to a liquid-liquid separator that responds to radical load disturbances.
2. The Relevant Technology
Water purification is an age-old activity that has been pursued to achieve both potable water and water for industrial use. With the rise of industrialization, water purification took on a new importance because industrial water usage generally involved discharging contaminated water into the environment. As concerns about the environment have increased, water discharged into the environment has been subjected to increasingly higher standards. Thus, increased efforts have been undertaken to identify methods of processing water to substantially reduce both dissolved and particulate pollutants.
One aspect of water purification that is particularly time consuming and/or equipment intensive is liquid-solid separation. Traditionally, settling ponds, or thickeners, have been used in which a large volume of particulate-containing water is allowed to reside in a quiescent state. With the force of gravity acting on the mixture, the particulate, even those in the Stokes flow regime, will separate from the liquid.
One disadvantage to the use of thickeners is that they have to be extremely large to have any significant flow capacity. Thus, their use is not practicable in crowded urban areas where the need for such water purification systems is often the greatest. Consequently, thickeners have been developed that allow for a continuous flow of particulate-containing liquid into the center of the thickener, producing a clarified supernatant liquid and a compacted sludge. The compacted sludge, exiting from the bottom of the thickener, typically has a water content that amounts to between 10 and 30 percent of total water being fed to the thickener.
Traditional thickeners have been improved in the last decade or so with the advent of the high-rate thickener. The high-rate thickener has a center feed well that extends below the mud line of the underflow material. Accordingly, all water entering the thickener must pass through the sludge which acts as a filter medium. By using the sludge as a filter, solid-liquid separation rates are increased, albeit only incrementally over that of traditional thickeners. Additionally, high-rate thickeners also must be very large and, consequently, also have large footprints, rendering their use impractical in many situations.
What is needed in the art is a system for clarifying a particulate-containing liquid that overcomes the space requirement and slow solid-liquid separation rates experienced in the prior art. Such apparatus, systems, and methods are disclosed and claimed herein.
Another aspect of separations includes liquid-liquid systems such as separating the oil and water from a sump in a machine shop or in a washing bay for trains or buses etc. Other liquid-liquid separation systems are utilized in the food industry where oil and water need separation. On of the problems in the prior art is the effect of load disturbances such as a surge of oil or water in a cleaning operation that upsets the balance of the oil/water feed ratio to the separator. Although the separator may be controlled to prevent one component from entering the wrong exit stream, a catastrophic surge of one component or the other cannot be controlled.
Another challenge to the liquid-liquid separator systems is a separation between two immiscible liquids with densities that vary by about 5% or less. Because of the closeness of the densities, separation becomes increasingly difficult.
What is needed in the art is a liquid-liquid separator that overcomes the problems of the prior art.
The present invention relates to separator systems, namely solid-liquid separators and liquid-liquid separators, that include a pressure vessel. The pressure vessel may be spherical or have an alternative configuration such as compound frusto-conical. The ends of the pressure vessel are mounted so that the vessel can be rapidly rotated about a longitudinal or rotational axis extending through the vessel. An inlet channel is configured at one end of the vessel through which a fluid mixture is pumped into the pressure vessel. An exit channel is provided at the opposite end of the vessel through which a select portion of the fluid mixture exits the vessel.
In a first embodiment of the present invention, the separator system includes a solid-liquid separator or clarifier. The solid-liquid separator is designed to separate particulate matter from a liquid. In this embodiment, a plurality of fins are disposed within the pressure vessel. The fins radially outwardly project from the longitudinal axis in parallel alignment with the longitudinal axis. At least a portion of each fin is disposed adjacent to the wall of the vessel so that the fins interact with the vessel wall to form a plurality of discrete flow channels that longitudinally extend through the vessel.
Radially outwardly projecting from the longitudinal axis in substantially perpendicular alignment with the longitudinal axis are a plurality of spaced apart discs. The discs intersect with the fins so as to partially block the flow channels. The discs channel the fluid flow away from the longitudinal axis of the vessel and along the vessel wall. The discs do not extend all the way to the outer wall of the pressure vessel, but leave a flow path between the perimeter of the discs and the wall of the pressure vessel.
Apart from their role in channeling fluid flow, the discs and the fins also provide structural support for each other. The discs and the fins are each configured with corresponding slots by which each fin matingly engages each disc, thereby facilitating assembly and providing mutual structural support. Hence, the discs and fins act as stays for each other as well as serving as flow diverters.
In one embodiment, underflow passages extend between select flow channels at the maximum diameter encircling the longitudinal axis. The underflow passages are configured by either truncating the end of a fin or providing holes or other orifices in or along the outer edge of a fin at desired locations. As discussed below, the underflow passages enable the separated particulate component to flow between adjacent flow channels so as to be extracted from the pressure vessel.
Disposed along the longitudinal axis of the vessel is an exit tube. The exit tube has an inlet end centrally disposed within the vessel and an outlet end fluid coupled with the exterior of the vessel. Radially outwardly projecting from the longitudinal axis are a plurality of extraction tubes. Each extraction tube has a first end fluid coupled with the inlet end of the exit tube and an opposing second end disposed a short distance from the wall of the vessel. The second end of each extraction tube is disposed within a corresponding flow channel. In one embodiment, there is an extraction tube for each flow channel. In an alternative embodiment, there may be only one extraction tube for two or more flow channels. In this latter embodiment, the underflow passages are used to provide fluid communication between flow channels that do not have an extraction tube and flow channels in which an extraction tube is disposed.
During operation of the solid-liquid separator, a liquid containing particulate matter is pump under pressure into the rotating vessel through the inlet channel. As the liquid enters the vessel, the liquid is channeled into one of the flow channels defined by the radial fins. The positioning of the disc within the flow channels forces the liquid to flow radially outward toward the vessel wall. At this location, the liquid is subject to the maximum centrifugal force produced by the rotating vessel. As a result of the applied centrifugal force, the heavier particulate matter within the liquid flows to and collects at the maximum inner diameter of the vessel encircling the longitudinal axis. The remaining liquid that is separated from the particulate matter continues to flow to the opposing end of the vessel. The clarified liquid subsequently exits the vessel through the outlet channel by way of a pressure relief valve.
The particulate matter, which is typically in the form of a fluid slurry, is removed from the vessel through the extraction tubes. That is, the particulate matter is permitted to collect within vessel until the collected particulate matter rises above the second end of the extraction tubes. At that point, a valve coupled with outlet end of the exit tube is opened. As a result of the pressure differential between the interior of the pressurized vessel and the surrounding environment, the particulate matter is sucked into the extraction tubes and then exits the vessel through the exit tube.
The solid-liquid separator is also configured to allow for the release of gases which may be introduced into the pressure vessel. Specifically, a small gas orifice is formed at the inlet end of the exit tube so as to establish fluid communication between the exit tube and vessel. Furthermore, a gas channel is formed that extends from the inlet channel to the gas orifice on the exit tube. The gas channel is formed along the longitudinal axis of the vessel and extends between the fins and through the discs. During operation, the lighter gas flows to the center of the vessel where it passes into the gas channel. When the valve is opened to facilitate removal of the particulate matter, the gas enters the exit tube through the orifice and exits with the particulate matter. In an alternative embodiment, the gas can be remove from the feed stream before it enters the solid-liquid separator by passing the stream through a commercially available needle valve or other device designed to remove gases from fluid streams.
The solid-liquid separator is particularly well suited to creating substantially quiescent solid-liquid separation cells (flow channels) between adjacent fins and against the inner wall of the rotating vessel. As such, turbulent transport phenomena is resisted and the emulsification of organic liquids, inorganic liquids and suspended solids is avoided. The solid-liquid separator also has distinct advantages over the prior art in that it significantly reduces the amount of liquid that is discharged with the solid particulate material. In particular, the percent of total water fed to the solid-liquid separator that exits as a portion of the solid particulate material is kept to a minimum.
In a second embodiment of the present invention, the separator system include a liquid-liquid separator. The liquid-liquid separator is designed to separate a mixture of two or more immiscible liquids, such as oil and water. The liquid-liquid separator is substantially identical to the solid-liquid separator discussed above. The primary distinction is that the discs have a plurality of perforations extending therethrough. The perforations enable the various liquids to pass directly through the discs as opposed to having to travel around the perimeter edge thereof. Optionally, however, the disc closest to the inlet channel of the vessel can be solid in order establish a flow regime that is directed toward the periphery of the vessel. In this embodiment, the perforated discs primarily function to support the fins.
During operation of the liquid-liquid separator, a mixture of immiscible liquids is pump under pressure into the rotating vessel through the inlet channel. As the liquid enters the vessel, the liquid is channeled into one of the flow channels defined by the radial fins. The positioning of the first solid discs within the flow channels forces the liquid to flow radially outward toward the vessel wall. As a result of the applied centrifugal force, the heavier liquid flows to and collects at the maximum inner diameter of the vessel encircling the longitudinal axis. The lighter liquid and any entrained gas flows to the center of the vessel. As a result, a boundary line is formed between the heavier liquid and the lighter liquid. The boundary line is selectively controlled within a defined range from the longitudinal axis.
During removal from the vessel, the lighter liquid and gas flow through the perforated discs and out the exit channel through a first valve. Since the gas exits with the lighter liquid, there is no need for a gas orifice communicating with the exit tube. The heavier liquid is drawn through the extraction tubes and exits through the exit tube by way of a second valve.
The liquid-liquid separator is operated under an inventive pressure differential system that maintains the boundary line, such as an oil/water interface, within a preferred range of radial distances from the longitudinal axis of the pressure vessel. Specifically, the inventive system allows the pressure vessel to handle catastrophic load disturbances, such as a shift from an oil/water mix to either 100% oil or 100% water, while maintaining the boundary line within the desired range.
It is therefore an object of the invention to provide a separator system that overcomes the problems of the prior art. It is also an object of one embodiment of the present invention to provide a separator system that accomplishes solid-liquid separation in a rotating vessel by use of centrifugal force and by directing the flow of the particulate-containing material. It is also an object of one embodiment of the invention to provide a separator system that accomplishes solid-liquid separation at a rate that is a quantum increase compared to traditional thickeners and high-rate thickeners while occupying a footprint that is practical for virtually any application. Another object of one embodiment of the present invention to provide a separator system that separates solids and liquids such that the solids portion has a liquid content of the total particulate-containing liquid feed material that is about five percent or less.
It is also an object of invention to provide an liquid-liquid separator system that overcomes the problems of the prior art. It is therefore an object of one embodiment of the invention to provide a separator system that accomplishes a liquid-liquid separation in a rotating pressure vessel by use of centrifugal force and applied pressure. It is also an object of one embodiment of the invention to provide a separator system that accomplishes liquid-liquid separation at a rate that is a quantum increase compared to traditional hydrocyclone separators while maintaining the ability to handle catastrophic load disturbances.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.